Multiplicities in the ordinary part of mod $p$ cohomology for $\mathrm{GL}_n(\mathbb{Q}_p)$

Abstract

Given a continuous ordinary Galois representation $\bar{\rho}:G_{\mathbb{Q}_p}\rightarrow\mathrm{GL}_n(\overline{\mathbb{F}}_p)$, Breuil and Herzig constructed an admissible smooth $\overline{\mathbb{F}}_p$-representation $\Pi(\bar{\rho})^{\mathrm{ord}}$ of $\mathrm{GL}_n(\mathbb{Q}_p)$ and showed that it occurs in certain globally defined mod $p$ cohomology spaces. By applying Taylor-Wiles patching to spaces of ordinary automorphic representations we prove that the indecomposable pieces of $\Pi(\bar{\rho})^{\mathrm{ord}}$ each occur with the same multiplicity at a well-chosen tame level.